1. Field of the Invention
The invention relates to a material suitable for the formation of an insulating film having a low dielectric constant. The invention also relates to a method for forming an insulating film having a low dielectric constant using the material, and electric parts or components which use an insulating film formed thereby. The electric parts or components include various parts or components in which a low dielectric constant insulating film is particularly advantageously used, such as semiconductor integrated circuits and circuit boards, as well as display devices and phase filters.
2. Description of the Related Art
By way of typical example, in multilayered wiring lines in multilayer wiring circuits represented by semiconductor integrated circuits, a decrease in signal transmission speed due to the parasitic capacitance of an insulating film is known.
The transmission speed of a signal is determined by the resistance of a wiring line and the parasitic capacitance between wiring lines. In general, a wiring delay (T) is influenced by a wiring resistance (R) and a capacitance (C) between wiring lines, and is represented by the following equation:T∝CR  (1)wherein the capacitance (C) between wiring lines has a relation with the dielectric constant (∈r) of an insulating film between the wiring lines, as represented by the following:C=∈0∈rS/d  (2)wherein ∈0 denotes the dielectric constant of a vacuum, S denotes an electrode area, and d denotes a distance between wiring lines.
Although at a distance between wiring lines of 1 micrometer or more, the influence of the wiring delay to the speed of the entire device was small, at a distance between wiring lines of 0.5 micrometer or less, the influence becomes not negligible. As is clear from the above equation, when the distance d between wiring lines becomes smaller due to the increase in degree of integration of semiconductor devices, the parasitic capacitance (capacitance between wiring lines) C increases. Although the capacitance of an insulating layer participating in the parasitic capacitance can be decreased by making the thickness of the wiring lines smaller and making the sectional area of the insulating film smaller, the smaller thickness of the wiring line gives rise to the increase in the resistance of the wiring line and, consequently, does not lead to a higher device speed. Thus, a decreased dielectric constant of an insulating film material itself is essential for a decrease in the parasitic capacitance and, if a circuit having a distance between wiring lines of 0.3 micrometer or smaller is formed in future, the effect of the parasitic capacitance between the wiring lines on the device speed will be large. Particularly, in the generation of a further decreased distance between the wiring lines, of 0.2 micrometer or smaller, it is expected that the dielectric constant of an insulating film will have a large effect on the signal transmission speed, and will be a large factor controlling the performance of semiconductor devices.
The insulating film materials mainly used in semiconductor integrated circuits, in which a low dielectric constant insulating film is particularly demanded, are silicon oxide (SiO2) and fluorine-doped SiO2 (FSG) produced by a chemical vapor deposition (CVD) process, and the like. It is known that the films formed of these materials have a dielectric constant of 3.6 at the lowest, although the value of dielectric constant varies depending on the conditions in which the film is deposited. Although insulating films based on silicon oxide formed by heat-treating a coated spin-on glass (SOG) are also known, they have a high moisture absorption and the dielectric constant of substantially 5 or higher.
Recently, polymeric materials based on polytetrafluoroethylene (PTFE) or a hydrocarbon have been proposed as insulating materials of low dielectric constant. However, the PTFE-based materials have problems in terms of thermal resistance and adhesion to other materials. On the other hand, of the hydrocarbon-based materials, materials based on linear hydrocarbons are regarded as having problems in terms of poor thermal resistance and variation in dielectric constant due to moisture absorption when polar groups are introduced to improve adhesion. Although materials based on aromatic hydrocarbons are advantageous in terms of thermal resistance relative to those based on linear hydrocarbons, their dielectric constant is 2.7 at the lowest.
In addition, there has been an attempt to provide an insulating film having a lower dielectric constant by making a film from a silicone material mixed with a compound to be removed at a low temperature, removing the compound from the film after the crosslinking of the silicone material, to thereby make the film have a low density. However, the resultant film has a small strength, and the technique of chemical mechanical polishing (CMP), which is a currently the standard technique for planarization, cannot be applied.